The present invention relates generally to systems for determining the outlet temperature of a turbocharger compressor for an internal combustion engine, and more specifically to such a system for estimating compressor outlet temperatures as a function of one or more engine operating conditions.
When combustion occurs in an environment with excess oxygen, peak combustion temperatures increase which leads to the formation of unwanted emissions, such as oxides of nitrogen (NOX). This problem is aggravated through the use of turbocharger machinery operable to increase the mass of fresh air flow, and hence increase the concentrations of oxygen and nitrogen present in the combustion chamber when temperatures are high during or after the combustion event.
One known technique for reducing unwanted emissions such as NOX involves introducing chemically inert gases into the fresh air flow stream for subsequent combustion. By thusly reducing the oxygen concentration of the resulting charge to be combusted, the fuel burns slower and peak combustion temperatures are accordingly reduced, thereby lowering the production of NOX. In an internal combustion engine environment, such chemically inert gases are readily abundant in the form of exhaust gases, and one known method for achieving the foregoing result is through the use of a so-called Exhaust Gas Recirculation (EGR) system operable to controllably introduce (i.e., recirculate) exhaust gas from the exhaust manifold into the fresh air stream flowing to the intake manifold.
EGR operation is typically not required under all engine operating conditions, and known EGR systems accordingly include a valve, commonly referred to as an EGR valve, for controllably introducing exhaust gas to the intake manifold. Through the use of an on-board microprocessor, control of the EGR valve is typically accomplished as a function of information supplied by a number of engine operational sensors.
In a turbocharged engine, a compressor component of the turbocharger typically supplies fresh air to the intake manifold of the engine via an intake conduit. An EGR system implemented in such a turbocharged engine supplies controlled amounts of exhaust gas to the intake manifold via the same intake conduit. In order to maintain the exhaust pressure above the intake manifold pressure to ensure positive EGR flow, turbochargers in EGR-based engines must typically operate at higher rotational speeds than in non-EGR-based engines. These high rotational speeds directly result in increased turbocharger outlet temperatures, and excessive heating of the compressor caused thereby could result in melting of the compressor housing and/or damage to the compressor wheel.
In turbocharged, EGR engines of the foregoing type, care must accordingly be taken to avoid generating excessive compressor outlet temperatures. However, in order to control and manage compressor outlet temperatures, it is generally necessary to have knowledge of current compressor outlet temperature conditions. Unfortunately, no production temperature sensors are currently known that can withstand the high temperatures typically encountered in the compressor outlet environment. What is therefore needed is system for accurately estimating compressor outlet temperature, so that the compressor outlet temperature can be maintained within a safe operating temperature range.
The foregoing shortcomings of the prior art are addressed by the present invention. In accordance with one aspect of the present invention, a system for estimating turbocharger compressor outlet temperature comprises a turbocharger having a compressor defining a compressor inlet and a compressor outlet fluidly coupled to an intake manifold of an internal combustion engine, a turbocharger speed sensor producing a turbocharger speed signal indicative of turbocharger rotational speed, means for determining air pressure within the compressor outlet and producing a first pressure signal corresponding thereto, a compressor inlet pressure sensor sensing air pressure within the compressor inlet and producing a second pressure signal corresponding thereto, means for determining a mass flow of fresh air entering the compressor inlet and producing a mass air flow signal corresponding thereto, and a control circuit computing a pressure ratio as a ratio of the first and second pressure signals, the control circuit estimating a temperature of the compressor outlet as a function of any two of the turbocharger speed signal, the mass air flow signal and the pressure ratio.
In accordance with another aspect of the present invention, a system for estimating turbocharger compressor outlet temperature comprises a turbocharger having a compressor defining a compressor inlet and a compressor outlet fluidly coupled to an intake manifold of an internal combustion engine, a turbocharger speed sensor producing a turbocharger speed signal indicative of turbocharger rotational speed, means for determining a mass flow of fresh air entering the compressor inlet and producing a mass air flow signal corresponding thereto, and a control circuit estimating a temperature of the compressor outlet as a function of the turbocharger speed signal and the mass air flow signal.
In accordance with yet another aspect of the present invention, a system for estimating turbocharger compressor outlet temperature comprises a turbocharger having a compressor defining a compressor inlet and a compressor outlet fluidly coupled to an intake manifold of an internal combustion engine, a turbocharger speed sensor producing a turbocharger speed signal indicative of turbocharger rotational speed, means for determining air pressure within the compressor outlet and producing first pressure signal corresponding thereto, a compressor inlet pressure sensor sensing air pressure within the compressor inlet and producing a second pressure signal corresponding thereto, and a control circuit computing a pressure ratio as a ratio of the first and second pressure signals, the control circuit estimating a temperature of the compressor outlet as a function of the turbocharger speed signal and the pressure ratio.
In accordance with still another aspect of the present invention, a system for estimating turbocharger compressor outlet temperature comprises a turbocharger having a compressor defining a compressor inlet and a compressor outlet fluidly coupled to an intake manifold of an internal combustion engine, means for determining a mass of fresh air entering the compressor inlet and producing a mass air flow signal corresponding thereto, means for determining air pressure within the compressor outlet and producing a first pressure signal corresponding thereto, a compressor inlet pressure sensor sensing air pressure within the compressor inlet and producing a second pressure signal corresponding thereto, and a control circuit computing a pressure ratio as a ratio of the first and second pressure signals, the control circuit estimating a temperature of the compressor outlet as a function of the mass air flow signal and the pressure ratio.
One object of the present invention is to provide a system and method for estimating turbocharger compressor outlet temperature.
Another object of the present invention is to provide a model-based system for estimating turbocharger compressor outlet temperature.
Yet another object of the present invention is to provide a system and method for controlling turbocharger compressor outlet temperature to limit the maximum outlet temperature to a predefined threshold temperature.
Still another object of the present invention is to provide system for achieving such control by modulating the swallowing capacity of the turbocharger turbine.
These and other objects of the present invention will become more apparent from the following description of the preferred embodiments.